Centrifugal governor speed control for electric motors

ABSTRACT

The specification discloses a speed control for an electric motor of the type including a centrifugal governor in which the governor comprises a rigid backing plate secured to the armature spindle of the motor and extending radially on opposite sides of the spindle and a flexible strip secured at its ends to the outer end parts of the backing plate and having weighted portions at or close to its extremities and an abutment part at its mid-point which engages means to open and close the contacts to the electric motor. The contacts may comprise a fixed contact and a movable contact, the movable contact being provided on the one arm of a two-armed lever which is pivotally mounted about an axis intermediate the two arms and the fixed contact member being mounted on a further arm pivoted about a further axis and adjustable in position relative to the movable contact by means of a manually operated cam to permit adjustment of the speed of the motor.

United States Patent Evans 1 May 2, 1972 541 CENTRIFUGAL GOVERNOR SPEED2,568,773 9/1951 Sparklin et a1 ..310/68 E x CONTROL FOR ELECTRIC MOTORS2,903,535 9/1959 Sparklin ..200/80 R 2,623,961 12/1952 Holstein ..310/69X [721 PhillP smutbndget England 2,719,945 10/1955 Tull ..200/80 R x 73Assign; Glenbum Engineering Limited, c/o 3,514,649 5/1970 Nomura..310/74 X vers, Dill & Pearman, Bank of Bermuda Bldg, Hamilto B dPrimary Examiner-James D. Trammell Assistant Examiner-Mark O. Budd [22]led: June 1970 AttorneyMerriam, Marshall, Shapiro & Klose 21 A 1. No.:50 827 I 1 pp 57 ABSTRACT [30] Foreign Application Priorit D Thespecification discloses a speed control for an electric motor of thetype including a centrifugal governor in which July 4, 1969 GreatBritain ..33724/69 the governor comprises a rigid backing plate securedto the mature spindle of the motor and extending radially on op- [52]U.S.C1. ..310/68 E, 200/80 R, 310/69, posite Sides of the spindle and aflexible Strip Secured at its 310/74 318/325 ends to the outer end partsof the backing plate and having Cl- I; portions at or c ose to extemities and an abu [58] Field ofSearc 8/0 318,325, ment part at its midpoim which engages means to open and l I close the contacts to theelectric motor. The contacts may 56 R t d comprise a fixed contact and amovable contact, the movable 1 e erences I e contact being provided onthe one arm of a two-armed lever UNn-ED STATES PATENTS which ispivotally mounted about an axis intermediate the two arms and the fixedcontact member being mounted on a 2,099,050 1 l/ 1937 Chamberlain..310/68 E X f th am i d about a f th i and adjustable in posi 333045832/ 1967 Hansen 1 1 --318/325 x tion relative to the movable contact bymeans of a manually 2,493,897 V1950 Pal et E x operated cam to permitadjustment of the speed of the motor. 2,623,962 12/1952 Holstein..310/68 E X 2,610,314 9/1952 Morse ..310/69 X 10 Claims, 5 DrawingFigures lCo 1a 1 Pat ented May 2, 1912 3 Sheets-Sheet 1 Pat ented May 2,1972 3 Sheets-Sheet 2 Pmnud May 2, 1972 3,660,703

3 Sheets-Sheet 5 CENTRIFUGAL GOVERNOR SPEED CONTROL FOR ELECTRIC MOTORSBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a speed control means for an electric motor.

The invention particularly relates to a speed control means for anelectric motor such as is used in domestic appliances, for example foodmixers, where control is provided to vary the motor speed between slowand fast limits so as to be capable of operating the appliance with themotor running at any speed in between the slow and fast limits.

The invention is particularly directed to electric motors for foodmixers where a speed control is desired in order to be able to operate afood mixer so that for certain jobs the heaters can rotate relativelyslowly and for other jobs rotate at faster speeds up to the fast limitof the device. Also, different appliances which can be attached to foodmixers require to be operated at different speeds and this also adds tothe requirement for speed control for the electric motors used in thistype of domestic appliance.

The invention is particularly concerned with a speed control means foran electric motor which comprises a governor on the electric motorspindle, which governor operates to open contact means in the electricsupply to the motor, there being a fixed contact means and a movablecontact means which is movable relativeto the fixed contact means andthe governor operates upon the movable contact means. The assembly offixed and movable contact means can be shifted by a graduatedhandcontrol to a desired position in relation to the governor inaccordance with the speed required.

In use, the motor speed increases towards its normal maximum runningspeed until the governor contacts the movable contact means and breaksthe circuit to the electric motor. So long as the fixed and movablecontact means assembly remains in this position the governor will havethe defect of repeatedly making and breaking the circuit to the electricmotor so as to keep the motor speed substantially at these desiredspeeds corresponding to the setting of the hand control which controlsthe movement of the assembly of movable and fixed contact means relativeto the governor.

2. Description of the Prior Art In this type of speed control means asused hitherto in food mixers the governor has comprised a flexiblespring strip secured to a collar on the motor spindle so that the stripextends radially on each side of the motor spindle and secured to eachouter end of the strip is a further flexible strip which extendsinwardly towards the motor spindle so that these two further flexiblestrips have their inner ends close to the motor spindle and the twostrips being bowed away from the single resilient backing strip. Theeffect of increase in speed of the motor spindle, due to the centrifugalforce acting on the inner ends of the two flexible strips, is to causethese strips to bow forwardly and outwardly away from the flexiblebacking strip and in so doing move a member mounted slidably upon themotor spindle to bring such member into engagement with the movablecontact means and thus initiate the breaking of the circuit to theelectric motor.

In practice, such a speed control means has certain disadvantagesbecause it does not enable the motor to operate at relatively low motorspindle speeds, for example below about 4,000 r.p.m., and there is alsoa limit to the maximum motor speed which can be provided by the speedcontrol means. This arises from the use of a combination of two flexiblestrips car ried by a flexible backing strip because at low speeds thebacking strip has too much rigidity and at the higher speeds it has toomuch flexibility and this limits the maximum and minimum speeds at whichthe speed control means can operate.

There is therefore a demand for a speed control means particularly forfood mixers which will allow the motor to operate at speeds above andbelow the limits set by the' above described and previously used speedcontrol means.

SUMMARY OF THE INVENTION An object of the invention is to provide a newand improved speed control means whereby the above mentioneddisadvantages are overcome or are reduced.

According to the invention, we provide a speed control means for anelectric motor comprising a centrifugal governor adapted to be rotatedby the electric motor and to open and close electric contacts in theelectric circuit tothe motor, the governor comprising a spindle adaptedto be rotated by the motor, a rigid backing plate fixedly secured to thespindle at the midpoint of the plate and extending radially on oppositesides of the spindle, a flexible strip secured at its ends to the outerend parts of the backing plate and having weighted portions at itsextremities and an abutment part at its mid-point, the main length ofthe flexible strip intermediate its ends being parallel or substantiallyparallel to the plane of the backing plate in the at-rest position andthe abutment part of the flexible strip being adapted to open and closethe contacts by flexing of the strip in the direction to move theabutment part away from the backing plate as a result of centrifugalforce acting on said weighted portions.

The weighted portions are conveniently formed by forming in the strip,near each of its ends, a loop which projects away from the backingplate.

The contacts may comprise a fixed contact and a movable contact and themovable contact may be provided on one arm of a two-armed member whichis pivotally mounted about an axis intermediate the two arms, the otherarm being engaged by the abutment portion and the fixed contact memberbeing on a further arm separately pivoted about said axis and saidfurther arm being acted upon by manually operable adjustment means tocause the further arm to move against spring resistance to enable thespeed of the motor to be adjusted.

By way of example, one embodiment of the invention will be describedhereinafter in detail with reference to the accompanying drawingswherein,

FIG. 1 is a side elevation of an electric motor including a speedcontrol means according to the invention,

FIG. 2 is a fragmentary underneath plan view of the motor of FIG. 1,

FIG. 3 is a cross-sectional view of part of the speed control means ofthe motor of FIG. 1 shown to an enlarged scale,

FIG. 4 is a section on the line 44 of FIG. 5, and,

FIG. 5 is a front elevation of the motor of FIG. 1 looking in thedirection of the arrow A.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, thereis shown an electric motor and part of the drive for the beaters of afood mixer. The motor is indicated generally at 10 and the gear box ofthe drive is shown at 11 and the drive collets for the heaters areindicated at 12.

The armature shaft of the motor carries a worm, indicated in chaindotted line at I3 in FIG. 2, which meshes with worm wheels shown inchain dotted line at 14 in FIG. 2 which are connected to the collets 12.

At the outer end thereof the motor armature shaft carries a collar 15upon which a rigid backing plate 16 is carried. The rigid backing plate16 extends radially away from the shaft on two diametrically oppositesides thereof. The backing plate 16 is preferably formed integrally withthe collar I5 as shown in FIG. 3 and a set screw 17 is provided tosecure the collar 15 to the shafi.

A flexible strip 18 is attached at its ends to the ends of the backingplate 16 by providing studs 19 on the backing plate which engage withinthe recesses 20 formed in the strip 18.

The strip [8 is preferably made from beryllium copper but this is notessential and other material having similar properties may be used. Neareach end the strip 18 has a loop 21 formed therein which constitutes aweighted portion to provide the centrifugal force to operate thegovernor constituted by the strip 18 and backing plate 16 when the shaftof the motor is rotated. Secured to the mid-point of the strip 18 and'ofthe strip 18.

The abutment surface 23, see FIG. 1, is engaged by an end portion of onearm 24 of a two-armed lever 25 which is pivoted to a bracket 26 fixedrelative to the motor 10, about an axis 27. The two-armed lever 25 has asecond arm 28 which carries a movable contact 29 connected by a wire 30to a fixed terminal tag 30a on the motor.

The arm 28 is acted upon by a coil tension spring 31 so that the arm 25is resiliently urged in an anti-clockwise direction about the axis 27,thus maintaining the arm 24 in contact with the surface 23.

Also mounted for rotation on the bracket 26 about the axis 27 is afurther arm 32 having a fixed contact 33 mounted thereon and acted uponby a second coil tension spring 34 .which also resiliently urges the arm32 in an anti-clockwise direction about the axis 27.

The arm 32 has a projecting portion 35 which engages a cam 36 connectedfor rotation to a hand engageable knurled disc 37 mounted for rotationon the bracket 26 about an axis 38.

The contact 33 constitutes the fixed contact and is connected by a wire39 to a terminal tag 40.

By way of explanation, the fixed contact 33 is termed fixed because atany set position of the speed control this contact remains stationaryand it is the movable contact 29 which is actuated by the governor, ashereinafter to be described. It will, of course, be appreciated from thefollowing description that the fixed contact 33 is moved to a desiredposition by the manual control but in any particular position to whichit is so moved it remains stationary for the purposes of speed control,which is why it is referred to herein as a fixed contact in order todistinguish it from the movable contact 29.

In use, referring now particularly to FIGS. 4 and 5, the hand-engageabledisc 37 is rotated so as to cause the cam 36 to move the arm 32 intoposition to give a desired speed of operation for the motor. The disc 37is graduated for this purose. Rotation of the disc 37 and hence of thecam 36 causes the arm 32 to rotate about the axis 27, rotation of thedisc 37 in a clockwise direction in FIG. 4 causing movement of the arm32 also in a clockwise direction and vice versa.

As the disc 37 is rotated in a clockwise direction in FIG. 4, the arm 32is also moved clockwise until the contact 33 engages the contact 29 andthe motor starts to operate. This position of contact corresponds to theslow speed of operation of the motor. If it is desired that the motoroperates at a higher speed, the disc 37 is continued to be rotated untilthe arm 32 is moved to the necessary position for the desired speed.

As the motor continues to rotate its speed of rotation increases and thecentrifugal force acting on the loop 21 causes the strip 18 to bend tomove the cam 16 in the direction away from the motor, so causing thesurface 23 to move the arm 24, thereby causing the two-armed lever 25 torotate clockwise about the axis 27, thus moving the movable contact 29out of engagement with the now fixed contact 33, thereby opening thecircuit to the electric motor and causing the electric motor to switchofi and hence slow down. As soon as the motor starts to slow down thecentrifugal force acting on the loops 21 decreases and so bowing of thestrip 18 decreases, thereby enabling the arm 25 to return to itsoriginal position under the influence of the coil tension spring 31,thus again closing the contacts 29, 33, and this continuous making andbreaking of if it is desired to change the speed of the motor it is onlyI necessary to adjust the disc 37, thus changing the null position ofthe making and breaking of the contacts 29 and 33.

In practice, it has been found that the use of a rigid backing plate 16in combination with the single flexible strip 18 forming the governor,enables the speed control to provide for a much wider range of motorspindle slpeeds than with governors used hitherto, and in particular yit enables the motor spindle to rotate at both higher and lower speedsthan has been possible with the arrangements hitherto.

I claim:

1. A speed control means for an electric motor comprising a centrifugalgovernor adapted to be rotated by the electric motor and to open and toclose electric contacts in the electric circuit to the motor, includingthe improvement wherein the governor comprises a spindle adapted to berotated by the motor, a rigid backing plate fixedly secured to an end ofthe spindle at the mid-point of the plate and extending diametrically ofthe spindle, a single flexible strip fixedly secured at its outer endsto the outer end parts of the backing plate and having weighted portionsat the extremities of the strip and positioned inwardly of the positionof securement of the strip to the backing plate and an abutment part atthe mid-point of the strip, the main length of the flexible stripintermediate its end being substantially parallel to the plane of thebacking plate in the at-rest position of the strip and the abutment partof the flexible strip being adapted to open and close the contacts byflexing of the strip respectively in the direction to move the abutmentpart away from and towards the backing plate as a result of centrifugalforce acting on said weighted portions.

2. A speed control means according to Claim 11 wherein the weightedportions are provided by forming the strip, at each of its ends andinwardly of the position of securement of the strip to the backingplate, with a loop which projects in the direction away from the backingplate.

3. A speed control means according to claim 2, wherein the strip isprovided with a projecting nose portion extending in the direction awayfrom the backing plate and having a transversely extending end surfacewhich provides the abutment part.

4. A speed control means according to claim 1, wherein the electriccontacts comprise a fixed contact and a movable contact, and the movablecontact is provided on one arm of a twoarmed member which is pivotallymounted about an axis intermediate the two arms, the other arm beingengaged by the abutment portion and the fixed contact member being on afurther arm separately pivoted about the axis and the further arm beingacted upon by manually operable adjustment means to cause the further amto move against spring resistance to enable the speed of the motor to beadjusted.

5. A speed control means according to claim 3, wherein the electriccontacts comprise a fixed contact and a movable contact, and the movablecontact is rovided on one arm of a twoarmed member which is pivotallymounted about an axis intermediate the two arms, the other arm beingengaged by the abutment portion and the fixed contact member being on afurther arm separately pivoted about the axis and the further arm beingacted upon by manually operable adjustment means to cause the furtherarm to move against spring resistance to enable the speed of the motorto be adjusted.

6. A speed control means according to claim 4, wherein said manuallyoperable adjustment means comprises a manually rotatable cam meansacting upon the further arm.

7. A speed control means according to claim 5, wherein said manuallyoperable adjustment means comprises a manually rotatable cam meansacting upon the further arm.

8. An electric motor including the improvement comprising a speedcontrol means as claimed in claim 1.

9. An electric motor according to claim 8, wherein the rigid backingplate is mounted on an extension of the armature of the motor.

10. An electric motor including the improvement comprising a speedcontrol means as claimed in claim 5.

1. A speed control means for an electric motor comprising a centrifugalgovernor adapted to be rotated by the electric motor and to open and toclose electric contacts in the electric circuit to the motor, includingthe improvement wherein the governor comprises a spindle adapted to berotated by the motor, a rigid backing plate fixedly secured to an end ofthe spindle at the mid-point of the plate and extending diametrically ofthe spindle, a single flexible strip fixedly secured at its outer endsto the outer end parts of the backing plate and having weighted portionsat the extremities of the strip and positioned inwardly of the positionof securement of the strip to the backing plate and an abutment part atthe mid-point of the strip, the main length of the flexible stripintermediate its end being substantially parallel to the plane of thebacking plate in the at-rest position of the strip and the abutment partof the flexible strip being adapted to open and close the contacts byflexing of the strip respectively in the direction to move the abutmentpart away from and towards the backing plate as a result of centrifugalforce acting on said weighted portions.
 2. A speed control meansaccording to Claim 11 wherein the weighted portions are provided byforming the strip, at each of its ends and inwardly of the position ofsecurement of the strip to the backing plate, with a loop which projectsin the direction away from the backing plate.
 3. A speed control meansaccording to claim 2, wherein the strip is provided with a projectingnose portion extending in the direction away from the backing plate andhaving a transversely extending end surface which provides the abutmentpArt.
 4. A speed control means according to claim 1, wherein theelectric contacts comprise a fixed contact and a movable contact, andthe movable contact is provided on one arm of a two-armed member whichis pivotally mounted about an axis intermediate the two arms, the otherarm being engaged by the abutment portion and the fixed contact memberbeing on a further arm separately pivoted about the axis and the furtherarm being acted upon by manually operable adjustment means to cause thefurther arm to move against spring resistance to enable the speed of themotor to be adjusted.
 5. A speed control means according to claim 3,wherein the electric contacts comprise a fixed contact and a movablecontact, and the movable contact is provided on one arm of a two-armedmember which is pivotally mounted about an axis intermediate the twoarms, the other arm being engaged by the abutment portion and the fixedcontact member being on a further arm separately pivoted about the axisand the further arm being acted upon by manually operable adjustmentmeans to cause the further arm to move against spring resistance toenable the speed of the motor to be adjusted.
 6. A speed control meansaccording to claim 4, wherein said manually operable adjustment meanscomprises a manually rotatable cam means acting upon the further arm. 7.A speed control means according to claim 5, wherein said manuallyoperable adjustment means comprises a manually rotatable cam meansacting upon the further arm.
 8. An electric motor including theimprovement comprising a speed control means as claimed in claim
 1. 9.An electric motor according to claim 8, wherein the rigid backing plateis mounted on an extension of the armature of the motor.
 10. An electricmotor including the improvement comprising a speed control means asclaimed in claim 5.